Dental articulators are mechanical devices which are used during the fabrication of dental restorations to simulate the movement of the human jaw. The human jaw comprises essentially an upper jaw or "maxilla" and a lower jaw or "mandible" together with accompanying muscles and ligaments. Movement of the human jaw is accomplished by movement of the mandible relative to the maxilla. The connection of the mandible to the maxilla is made by two opposing (left and right) ball and socket type joints at the posterior of the jaw. The maxilla includes the two opposing fossae defining downturned sockets, while the mandible includes two enlarged bone portions or "balls" known as condyles. The ball and socket connection between each human fossa and condyle is referred to as a temporomandibular joint.
Movement of the human mandible results from two types of movement within the temporomandibular joint: rotational movement about different axes through the condyles and translational movement of the condyles themselves. A protrusive movement, where the mandible slides forward to align the upper and lower (maxillary and mandibular) teeth, is an example of a primarily translational movement of the condyles within the temporomandibular joint. The rotational movement of the mandible can occur about three different axes. First, the mandible may rotate about a horizontal or "hinge" axis which passes through the two separate condyles within the opposing temporomandibular joints. Second, during a lateral excursion in which the mandible moves toward one side (the working side), there is rotational movement of the mandible about a vertical axis which passes through the condyle on the working side (i.e., for a left lateral excursion, the mandible rotates about a vertical axis passing through the left condyle). Third, during a lateral excursion, the non-working condyle tends to drop down or move in a downward arc so that the condyle on the working side rotates about a second horizontal or "sagittal" axis perpendicular to both the hinge axis and the vertical axis (i.e., for a left lateral excursion, the mandible rotates about a sagittal axis passing through the left condyle).
The range of movement of a patient's mandible is determined by, among other things, the temporomandibular joints of the patient's jaw and the guiding contact between the patient's upper and lower anterior teeth. During the fabrication of dental restorations, a dentist must attempt to simulate as closely as possible the movement of the patient's mandible to both diagnose interferences between the patient's teeth and to check the fit of fabricated dental restorations prior to fitting the patient with the restorations.
An articulator is typically used to simulate the movement path of the patient's fossa and condyle pairs. Articulators commonly include upper and lower frame members connected together about at least a hinge axis for relative rotational movement. Thus, once casts of a patient's upper and lower teeth are attached to the upper and lower articulator frame members, respectively, two of the primary determinants of the patient's mandibular movement are recreated to help diagnose potential interferences between the patient's existing teeth and to aid in checking the fit of dental restorations.
Prior art articulators vary in complexity (and thus in the degree of accuracy with which they reproduce mandibular movement) from simple "hinge" articulators (typically used for partial restorations) to fully adjustable articulators (typically used for full mouth reconstructions). The simpler articulators are typically capable of little more than an opening about the hinge axis. Rotation of the lower frame member about the remaining two axes (the vertical and the sagittal) is either limited or prohibited, as is translational movement of the lower frame member. Thus, lateral excursions and protrusive movements of the mandible are not accurately simulated by these types of simple articulators. Semi-adjustable articulators allow for limited rotation and translation of the lower frame member relative to the upper frame member by mechanically recreating the human temporomandibular joints, typically through the use of spring biased hinges. Unfortunately, these mechanical temporomandibular joints do not accurately reproduce the complicated movements of the human condyles within the fossae of the maxilla. Indeed, many prior art articulators "invert" these functional elements, placing the condylar path simulating the fossa on the lower frame member and the condylar element simulating the condyle on the upper frame member, to simplify the operation of the articulator. Such an inversion further limits the accuracy of the articulator. Thus, a current need exists for a simple dental articulator which accurately reproduces a patient's mandibular movement.
It is with regard to this background information that the improvements available from the present invention have evolved.